Fantastic video explaining Diffie-Hallman key exchange alogrithm used in asymetric gyptography in a simple way.

https://www.youtube.com/watch?v=YEBfamv-_do

Thanks to Khan academy for yet another lessions.

This video explain the RSA algorithme https://www.youtube.com/watch?v=Z8M2BTscoD4

And her you find an example where the Euler Totient function is calculated in an other way https://www.youtube.com/watch?v=kYasb426Yjk

For sysetric encryption I find this video wery good https://www.youtube.com/watch?v=jKkZ9-Ij6Hs